Parity has struck out in the NFL. There are no Cinderella cries of “Why not us?” in Denver, in New England, in Seattle or in San Francisco. There are no Davids left chasing the Lombardi Trophy, only Goliaths.

Every summer, training camps open with 32 teams — check that, the Jaguars, Browns, Raiders, Jets, and Bills were all blowing smoke at their respective fan bases — harboring Super Bowl dreams. Only six months earlier, Ray Lewis and the Ravens finished writing a fairy tale for the ages, remember? Only a year before that, Eli Manning and the Giants shocked the Patriots again in Super Bowl XLVI.

Philip Rivers and the Chargers undoubtedly would have had Pete Rozelle smiling down from parity heaven, but they ultimately betrayed the Any Given Sunday football gods in Denver on Sunday.

What in the world of Roger Goodell is going on here?

Aren’t we entitled to cheer on a team like the Super Bowl III Jets every year or two?

Why is the chalk, the four favorites, Vegas’ best bets — at the start of the season, Broncos and 49ers were +600, Seahawks +850, Patriots +1,000 via Oddshark.com — fighting it out to get to MetLife Stadium and Super Bowl XLVIII?

Well, for starters, the Broncos and Patriots have the two best quarterbacks of this generation in Peyton Manning and Tom Brady. Manning was another year removed from his four neck-fusion surgeries, so you figured his 37-year-old arm would come back stronger. And the addition of Wes Welker and emergence of tight end Julius Thomas helped Manning to a record 55-touchdown season that enabled the Broncos to withstand the loss of Von Miller and health issues of coach John Fox.

But how and why are the Patriots still standing? One word: genius. One name: Bill Belichick. And he has done it all without Tim Tebow! Aaron Hernandez is out of sight and allegedly out of his mind. Rob Gronkowski was Halley’s Comet. Vince Wilfork and Jerod Mayo were lost. And Welker ran into Manning’s warm embrace.

It helped there was no one to threaten them in the AFC East. Both the Jets (Geno Smith) and Bills (EJ Manuel) were rebuilding, and the Dolphins had to weather a bullying storm. So Belichick got himself a first-round bye and home divisional playoff game, and Brady, at 36, still makes everyone around him better. Apparently including LeGarrette Blount, the 250-pound horse who ran over Andrew Luck’s Colts. And definitely Julian Edelman, who did more to help fill the Welker void than the more-advertised Danny Amendola.

It also helped Matt Schaub was throwing pick-sixes and they were burning his jersey in Houston, which was expecting its first Super Bowl championship. It helped Ravens general manager Ozzie Newsome traded Anquan Boldin to the 49ers, tight end Dennis Pitta missed most of the season, the offensive line couldn’t block for a diminished Ray Rice and Joe Flacco isn’t Brady. It helped Andy Dalton can’t win a playoff game. It helped Luck fashioned that epic comeback and knocked Andy Reid and the Chiefs out of the way.

The 49ers were Super Bowl runners-up a year ago. But their best pass rusher, Aldon Smith, had substance-abuse issues. And Colin Kaepernick missed wide receiver Michael Crabtree, who was out most of the season rehabbing his Achilles. But the offensive line is arguably the best in the sport, Boldin added toughness and clutchness and Jim Harbaugh is an elite coach.

It helped Matt Ryan was sabotaged by Roddy White’s injury issues and the early loss early of Julio Jones, and the Falcons simply weren’t tough enough in the trenches. It helped the Giants made a mockery of the infamous countdown clock, Hakeem Nicks, Jason Pierre-Paul and David Wilson endured nightmare seasons, the offensive line was ravaged by injuries and Eli Manning threw the ball to the other guys. It helped RG3 was more RG-Me and Tony Romo was Tony Oh No and Chip Kelly, Nick Foles and the Eagles stole the NFC East.

It helped Aaron Rodgers’ broken collarbone and Clay Mathews’ broken thumb left the Packers vulnerable, and it helped the undisciplined, underachieving Matthew Stafford Lions turned into Discount Daaaable Wrecks and the Bears were anything but Monsters of the Midway with the division there for the taking.

It helped Cam Newton was anything but Superman in his first playoff game. It helped Drew Brees and Sean Payton had to deal with the Seahawks and their deafening 12th Man in the divisional round.

Why are the Seahawks here? Pete Carroll has made them believe. Marshawn Lynch is Beast Mode, as is the Legion of Boom secondary. Russell Wilson is a resourceful leader and winner, mature beyond his years. The Seahawks feed off their 12th Man, and vice versa. They lost in the playoffs a year ago to the Falcons in Atlanta, so they are playoff-hardened and hungry.

So it will be Seahawks-Broncos in the Super Bowl. Or Seahawks-Patriots. Or 49ers-Broncos. Or 49ers-Patriots.